Android 6.0 marshmallow - app issues

After updating from Lollipop to Marshmallow, I see that most of my installed apps are not running, or has some or the other issue.
How do I get out of these?
Why are all the apps not compatible on marshmallow?
Will there be any update from Google for these issues?

Are you talking about the core Google apps, or are you referring to 3rd party apps? You may want to check to see if the apps that aren't working have been updated/optimized for running on Android 6.0, yet? Look at each apps page in the Play Store to see when the latest update was pushed out for the app and if the changelog for the app mentions being updated for 6.0. If the apps haven't been updated, then that may be the problem and you could then contact the developer of the app to see if they're working on a update for Marshmallow.

Thanks for the reply, It seems like some of the apps after updating worked, and some apps had to be un-installed and installd back again from the play store. But still some apps are crashing, may be as u said, need 2 contact that app dev team to see if there is support on MarshMallow.